Process for forming iron whiskers of uniform high quality

ABSTRACT

This invention provides a process for growing single, uniaxial crystals of iron having uniform physical properties, the process consisting essentially of placing an iron halide in a boat, heating the boat and its contents to a temperature below the Curie point of iron in a flow of hydrogen gas and applying a magnetic field to the zone surrounding the boat during the growth of the resulting crystals.

United States Patent Inventor Iqbal Ahmad Elnora, N.Y. Appl. No. 868,274 Filed Oct. 8, 196 9 V Continuation-impart 0! Ser. No.

673,2, Oct. 5, 1967, abandoned Patented Sept. 21, I971 Assignee The United States of America as represented the Secretary oi the Army PROCESS FOR FORMING IRON WIIISKERS OF UNIFORM HIGH QUALITY 9 Claims, 3 Drawing Figs. i

US. Cl 148/16, 7 5/05 BA Int. Cl 801i 17/32 Field of Search 148/ l .6;

75/O.5 AA, 0.5 BA

1 [56] References Cited UNITED STATES PATENTS 2,842,469 7/1958 Pullman et a1. 148/].6 2,884,11 l9 4/1959 Fabian et a1. 75/.5 3,132,022 5/1964 Luborsky et a1. 75/.5 3,144,353 8/1964 Allan 61 a]. 148/].6 3,206,333 9/1965 Miller et al. 148/105 Primary Examiner--L. Dewayne Rutledge Assistant Examiner-E. L. Weise Anorneys- Harry M. Saragovitz, Edward J. Kelly, Herbert Berl and Albert E. Arnold, Jr.

ABSTRACT: This invention provides a process for growing single, uniaxial crystals of iron having uniform physical properties, the process consisting essentially of placing an iron halide in a boat, heating the boat and its contents to a temperature below the Curie point of iron in a flow of hydrogen gas and applying a magnetic field to the zone surrounding the boat during the growth ol'the resulting crystals.

PROCESS FOR FORMING IRON WHISKERS OF UNIFORM HIGH QUALITY PROCESS FOR FORMING IRON WHISKERS OF UNIFORM HIGH QUALITY The above-identified patent US. application is a continuation-in-part of applicants previously filed US. Pat. application Ser. No. 673,224, filed Oct. 5, 1967, now abandoned.

SPECIFICATION The invention described herein may be manufactured, and used by or for the Government for Governmental purposes without the payment to me of any royalty thereon.

BACKGROUND OF THE INVENTION Because of their high internal and surface perfection and, consequently unusually high tensile properties, filamentary single crystals, hereinafter called whiskers, of metals and their compounds have drawn considerable interest during the last decade. A number of workers have grown iron whiskers through the reduction of the halides of iron with hydrogen and have studied their physical and mechanical properties. In all of these studies, whiskers are found to grow in all directions; have gross defects such as kinks. branching and nonuniformity of cross section and have different crystallographic orientation. Consequently, even in the same batch, the properties of individual whiskers vary widely.

It is the object of this invention to provide a process of growing iron whiskers of uniaxial structure and uniform physical properties by applying a magnetic field to the zone in which the crystals are grown and carefully controlling within specific limits the strength of the magnetic field, the temperature to which the halide is heated and the rate at which hydrogen gas is passed over the halide. The specific nature of the invention as well as other objects and advantages thereof will clearly appear from a description of a preferred embodiment as shown in the accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a longitudinally cross-sectioned top view of the apparatus used in the preferred embodiment of the crystal-forming process with the gas control valve shown adjusted for passing hydrogen into the chamber and the boat located in the reaction zone thereof;

FIG. 2 is an enlarged, fragmentary section of the chamber at the reaction zone showing the whiskers formed on the inside of the boat and on the spiral; and

FIG. 3 is a section taken along line 33 of FIG. 2.

DESCRIPTION OF A PREFERRED EMBODIMENT The apparatus consists of a cylindrical chamber 12, such as a vycore tube, having a central reaction zone 14 which is surrounded by a heating coil 16. Reaction zone I4 is located between poles 20 of an electromagnet 22 which is adjustable as to produce a magnetic field of the order of 3,500 to 5,500 oersteds within the reaction zone. A closed end tube 24 extends coaxially from one end of chamber 12 and such tube includes a branch 26 in which there is located a valve 28 arranged for selective passage of argon or hydrogen gas from sources not shown into chamber 12. The selected gas passes from chamber 12 through an outlet 30 in the opposite end thereof, and a thermocouple 32 extends into chamber 12 from such opposite end to record the temperature in reaction zone 14.

A boat 34 of U configuration in cross section and of a nonmagnetic material such as alumina is slidingly mounted in chamber l2 so that the sides of the boat are disposed perpendicular to the magnetic field. Boat 34 is connected by a rod 36 to an iron slug 38 slidingly disposed in tube 24 and a magnet 40 acts on slug 38 for moving the boat into and out of reaction zone 14. To provide areas for additional nucleation sites, a spiral 42 of a nonmagnetic material, such as stainless steel, is placed longitudinally in boat 34.

In the preferred embodiment of this invention, the process begins by placing l0 g. of FeCl,.4I-I O (crushed) in boat 34, positioning the boat in chamber 12 outside of reaction zone 14, and turning valve 26 to permit the flow of argon gas through the chamber. Heating coil 16 is then energized. When a constant temperature of 680 C., as recorded by thermocouple 32, is achieved, electromagnet 22 is energized and adjusted to produce approximately 4,000 oersteds within reaction zone 14. Valve 26 is next turned to change the' flow of gas into chamber 12 from argon to hydrogen which is regulated to flow at a rate of 200 cc./min. and boat 34 is then moved into reaction zone 14 so that the sides thereof are perpendicular to the magnetic field produced between poles 20. After about 15 minutes, boat 34 is moved out of reaction zone 14 and electromagnet 22 and heating coil 16 are turned off. When chamber 12 has achieved the ambient temperature, boat 34 is removed from chamber 12.

The resulting whiskers 44, which have grown from nucleation sites on the sides of boat 34 and on spiral 42, are aligned parallel to the magnetic field produced between poles 20 of electromagnetic 22 and are of uniform physical characteristics. X-ray diffraction of whiskers 44 show them to be single crystals and optical observation of their cross section indicate them to be of similar crystallographic orientation. The whiskers, too, have a consistently high surface reflectively and a very fine 10 microns) diameter.

The morphology of whiskers 44 can be controlled by controlling the supersaturation of the iron chloride vapor produced in reaction zone 14, through the regulated relationship between the temperature therein and the flow of hydrogen gas therethrough, which may be varied between l00 cc. and 300 cc. per minute, and the strength of the magnetic field. The temperature is regulatable between 600 and 770 C.; the Curie point of iron being considered to be 769 to 770 C; and it is found that the range of the magnetic field strength can be adjusted between 3,500-5,500 oersteds and be effective with the strength of the magnetic field and the flow of hydrogen gas being determinable in part by the geometry of chamber 12. The length of whiskers 44 is determinable by the geometry of boat 34 and the time in which the boat is located in reaction zone 14.

It is obvious that the same process can be used in produce whiskers of other magnetic materials.

I wish it to be known that I do not desire to be limited to the exact details of construction shown and described, for obvious modifications will occur to a person skilled in the art.

I claim:

1. In a process of growing single-crystal whiskers of iron by passing hydrogen gas over a halide of iron placed within a boat located in a reaction zone of a chamber heated to a constant temperature below the Curie point of iron, the improvement comprising the step of applying a magnetic field of the order of 3,500 to 5,500 oersteds perpendicular to the reaction zone during growth of the whiskers whereby the resulting whiskers are uniformly of uniaxial structure with similar crystallographic orientation and extend orderly from nucleation sites in the boat.

2. The process as defined in claim 1 wherein the halide of iron is FeCl .4H O.

3. The process as defined in claim 2 wherein the reaction zone of the chamber is heated to a temperature in the range from 600 to 770 C.

4. The process as defined in claim 2 wherein the reaction zone is heated to approximately 680 C.

5. The process as defined in claim 11 wherein the magnetic field applied to the zone surrounding the boat is of the order of 4,000 oersteds.

6. The process as defined in claim 1. wherein the boat is of U-configuration in cross section and includes the step of placing the boat in the reaction zone so that the sides are disposed perpendicular to the magnetic field.

7. A process of growing single-crystal iron whiskers comprising the steps of placing crushed pieces of FeCl .4H 0 in a boat of U-shaped configuration in cross section and of a nonmagnetic material, positioning the boat in a chamber having a that the sides thereof are perpendicular to the magnetic field. reaction zone, heating the chamber to a constant temperature 3 The process as d fi d in claim 7 wherein said reaction beiow the Cune Polm of flowing argon gas through the zone is heated to a temperature in the range from 600 to 770 chamber, applying a magnetic field of the order of 3,500 to 5,500 oersteds perpendicular to the reaction zone, flowing hydrogen gas through the reaction zone instead of the argon gas, moving the boat into the reaction zone so as to be under the influence of the magnetic field, and positioning the boat so 9. The process as defined in claim 8 wherein said reaction zone temperature is maintained at approximately 680 C. 

2. The process as defined in claim 1 wherein the halide of iron is FeCl2.4H2O.
 3. The process as defined in claim 2 wherein the reaction zone of the chamber is heated to a temperature in the range from 600* to 770* C.
 4. The process as defined in claim 2 wherein the reaction zone is heated to approximately 680* C.
 5. The process as defined in claim 1 wherein the magnetic field applied to the zone surrounding the boat is of the order of 4,000 oersteds.
 6. The process as defined in claim 1 wherein the boat is of U-configuration in cross section and includes the step of placing the boat in the reaction zone so that the sides are disposed perpendicular to the magnetic field.
 7. A process of growing single-crystal iron whiskers comprising the steps of placing crushed pieces of FeCl2.4H2O in a boat of U-shaped configuration in cross section and of a nonmagnetic material, positioning the boat in a chamber having a reaction zone, heating the chamber to a constant temperature below the Curie point of iron, flowing argon gas through the chamber, applying a magnetic field of the order of 3,500 to 5,500 oersteds perpendicular to the reaction zone, flowing hydrogen gas through the reaction zone instead of the argon gas, moving the boat into the reaction zone so as to be under the influence of the magnetic field, and positioning the boat so that the sides thereof are perpendicular to the magnetic field.
 8. The process as defined in claim 7 wherein said reaction zone is heated to a temperature in the range from 600* to 770* C.
 9. The process as defined in claim 8 wherein said reaction zone temperature is maintained at approximately 680* C. 